This application claims priority under 35 U.S.C. .sctn.119 [and/or .sctn.365] to "The Throttle Valve Controller", Application No. H09-172491 filed in JAPAN on Jun. 27, 1997, the entire content of which is herein incorporated by reference.
This invention relates to a throttle valve controller for electronically controlling the opening of the throttle valve. More particularly, this invention relates to a throttle valve controller using a D.C. motor to drive the throttle valve.
A conventional throttle valve controller uses a D.C. motor to drive the throttle valve. Such a D.C. motor is driven by a feed back controller employing a PID control (e.g., proportional integral and derivative control) based on a difference between a target position and an actual position. However, such a PID control may become rough in the long term due to varied friction forces affecting the slipping mechanism such as a reduction mechanism. In other words, response of the throttle valve may be deteriorated due to the variable friction forces of the slipping mechanism.
To solve such problems, various solutions have been proposed. For example, Japanese Laid-Open Patent No. H02-125937 discloses a scheme to add a friction compensator to the PID control. This conventional scheme will control the throttle valve more accurately due to compensated motor torque.
Japanese Laid-Open Patent No. H07-259618 discloses a pulsed current supplied to the motor. The pulsed current will act for the throttle valve to draw a small hysteresis loop till the throttle valve reaches the target position. The pulsed current will compensate the hysteresis torque of the mechanism that corresponds to the friction force of the mechanism.
Japanese Laid-Open Patent No. H07-332136 discloses an increased gain for the proportional control which is a part of the PID control in order to increase torque of the electric motor while the actual position of the throttle valve is close to the target position. The throttle valve is moved to the target position accurately due to increased torque of the electric motor.
Although various conventional schemes are proposed to compensate the friction force of the throttle valve control system, these conventional schemes may not properly control the throttle valve at certain areas such as near the fully closed position.
Japanese Laid-Open Patent Publication No. H07-332136 increases the gain for the proportional control with respect to a minor displacement of the throttle valve. However, the throttle valve may not be moved effectively when the increased gain is not high enough. Further, the throttle valve may be vibrated by hunting in case the increased gain is too high since this scheme does not consider any difference between dynamic and static friction forces.
Japanese Laid-Open Patent Publication No. H07-259618 always vibrates the throttle valve. Therefore, the throttle valve may not be moved effectively or may be vibrated by hunting due to the same reason as Japanese Laid-Open Patent Publication No. H07-332136.
Japanese Laid-Open Patent Publication No. H02-125937 distinguishes static friction force from dynamic friction force. However, the throttle valve may be overshot significantly upon switching from static friction control to dynamic friction control.
In the above conventional schemes, the PID controller continuously supplies electric power to the motor to follow the target position of the throttle valve within a set control period. Therefore, the throttle valve is kept moving due to a fixed amount of the electric power supplied to the motor within the set control period. Accordingly, the throttle valve may be opened excessively when the throttle valve passes over the target position. At the subsequent control period, the throttle valve will be closed by the reversed power supplied to the motor to get the target position. However, if this is the case, the throttle valve may be closed excessively in case the throttle valve again passes over the target position in the subsequent control period. The longer the control period, a more significant problem will occur so that the throttle valve is kept vibrating due to hunting or the throttle valve may be opened extremely so wide due to the overshoot.
To solve the above conventional problems, the control period may be shortened to increase resolution of the controller. However, a more precise controller is required to increase the resolution. As a result, the controller may be too expensive to be employed for typical applications.
Accordingly, a feature of the present invention is to solve the above conventional problems.